Method for extracting and separating zirconium and hafnium in nitric acid medium

ABSTRACT

A method for extracting and separating zirconium and hafnium in nitric acid medium mainly includes extraction of acidic raw liquid containing zirconium compounds with a synergistic extraction system consisting of DIBK and a phosphonic acids extraction agent, so that the zirconium goes to the aqueous phase and the hafnium goes to the organic phase, thus achieving separation. There is no need of use of toxic substance throughout the process.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application based on international patent application No. PCT/CN2018/072340, filed on Jan. 12, 2018 and entitled “Method for Extracting and Separating Zirconium and Hafnium in Nitric Acid Medium” and the international patent application claims the priority of the Chinese patent application No. 2018100052447, filed with the Chinese Patent Office on Jan. 3, 2018, and entitled “Method for Extracting and Separating Zirconium and Hafnium in Nitric Acid Medium”, which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to the technical field of purification, and specifically to a method for extracting and separating zirconium and hafnium in nitric acid medium.

BACKGROUND ART

Zirconium and hafnium are symbiotic in the nature. As commercially available zirconium-containing chemicals normally contain a relatively low hafnium content (m_(Hf)/m_((Zr+Hf))) (generally at 1˜3%), it would be relatively largely advantageous to use an extraction agent by which hafnium is preferentially extracted in the separation. Due to “lanthanide contraction”, zirconium and hafnium have substantially identical atomic radius and ionic radius, and very similar physical and chemical properties, so it is very hard to separate them from each other. They are seen as two of the elements that are most difficult to separate in the periodic table of elements. However, zirconium and hafnium have different nuclear performances. With a small thermal neutron absorbing cross-section, zirconium is widely used as cladding and structure materials of nuclear reactor. It is required for nuclear grade zirconium that hafnium content should be lower than 0.01%. In contrast, hafnium has a large thermal neutron absorbing cross-section and is mainly used in the neutron control rod in the nuclear reaction. It is required for nuclear grade hafnium that zirconium content should be lower than 2%. Therefore, separating zirconium and hafnium is the key to obtain nuclear grade zirconium and nuclear grade hafnium materials.

Nuclear power is an economic and efficient clean energy which does not cause emission of sulfur dioxide, smoke, dust, nitrogen oxides or carbon dioxide. Replacing partial thermal power with nuclear power not only reduces exploitation, transportation and total combustion capacity of coal, but also makes effective contribution to reducing emission of pollutants in electric power industry. Moreover, it is an important measure to slow down global greenhouse effect. Countries have been making a great effort to develop nuclear power in recent years, which facilitates the development and concern of separation technologies of zirconium and hafnium. Many separation methods of zirconium and hafnium have been developed, e.g. molten salt rectification method, ion exchange method and solvent extraction method. Solvent extraction method becomes the main method for separating zirconium and hafnium due to a series of outstanding advantages, e.g. high equilibrium speed, good separation result, large handling capacity, ease of continuous operation and low cost. In term of extraction system, there is neutral extraction system, acidic extraction system, basic extraction system, chelation extraction system and synergistic extraction system. Currently, among reported extraction agents and extraction systems, only MIBK, Cyanex 301, Cyanex 302 and D2EHPA show properties of preferential extraction of hafnium present at a relatively low content in zirconium-containing chemicals. All of them, except MIBK, are used for extraction of diluted solution (zirconium <10 g/L). This is not desired for industrial application.

MIBK method was developed and used for industrial production in 1970s in USA. Nearly ⅔ of nuclear grade zirconium and hafnium in the world are separated by such method. MIBK method comprises preferentially extracting hafnium present at a low content in zirconium and hafnium containing hydrochloric acid medium under a condition in the presence of SCN⁻, and zirconium with a high content is left in the aqueous phase. In this way, zirconium is separated from hafnium (with a separation coefficient up to about 9 for zirconium and hafnium). The extraction agent has a large capacity and a high efficiency. However, MIBK method has following defects. (1) MIBK has a solubility up to 1.7 wt % in water (one of the extraction agents with highest solubility in water), which means a high solvent loss. (2) It involves use of unstable thiocyanic acid (and thiocyanates) which is likely to decompose into toxic decomposition products e.g. hydrogen sulfide, methyl mercaptan, CN⁻, etc. under acidic condition, which contaminate the environment. (3) MIBK has some smell which degrades the environment in the workshop. (4) MIBK has a low flash point and thus is likely to start a fire. The drawbacks of MIBK necessitate improvement or replacement.

Diisobutyl ketone (DIBK) is a neutral oxygen-containing extraction agent which has a similar structure to MIBK. They have similar extraction performances and extraction mechanisms. The difference in structure leads to their difference in properties as extraction agents. For example, DIBK has a flash point of 47° C., whereas MIBK has a flash point of only 22.78° C.; the water solubility of DIBK is 0.043 wt %, whereas that of MIBK is as high as 1.7 wt %. It's exactly these defects that restrain MIBK method from industrial application.

Currently, thiocyanic acid or salts thereof are required if diisobutyl ketone (DIBK) is used as an extraction agent. For their high toxicity, thiocyanic acid or salts thereof are not environmentally friendly during separation process.

SUMMARY

A purpose of the present disclosure is to provide a method for extracting and separating zirconium and hafnium in nitric acid medium. There is no need of using toxic substances during separation process in this method and thus enables clean the separation process of zirconium and hafnium.

Another purpose of the present disclosure is to provide a method for extracting and separating zirconium and hafnium in nitric acid medium, which may be applied to separation of zirconium and hafnium in hafnium-containing zirconium compounds.

The embodiments of the present invention are implemented in the following way.

The first aspect of the present disclosure is to perform extraction by mixing an extraction agent with acidic raw liquid formed by mixing a zirconium-containing chemical and nitric acid, mix the raffinate obtained by the phase separation of the extraction with a base solution to give zirconium hydroxide precipitate, strip the hafnium-containing loaded organic phase with a carbonate solution, mix the strip liquid (i.e. the liquid obtained by the stripping) with base to give hafnium hydroxide precipitate, roast the zirconium hydroxide precipitate and the hafnium hydroxide precipitate. The extraction agent comprises a mixture composed of diisobutyl ketone (DIBK) and phosphonic acids extraction agent (containing C—P bond).

Preferably, the phosphonic acids extraction agent (containing C—P bond) is at least one selected from the group consisting of Cyanex921, Cyanex923, Cyanex925 and Cyanex572.

Preferably, a pre-extraction of nitric acid with the extraction agent is performed before the extraction.

Preferably, the nitric acid has a concentration of 2.0˜6.0 mol/L in the pre-extraction, and/or the extraction agent has a volume equal to that of the nitric acid in the pre-extraction.

Preferably, the acidic raw liquid further comprises an inorganic salt.

The second aspect of the present disclosure is to mix a zirconium-containing chemical and nitric acid to make an acidic raw liquid, perform extraction of the acidic raw liquid with an extraction agent to give a raffinate and a hafnium-containing loaded organic phase after the phase separation of the extraction, mix the raffinate with a base solution to give zirconium hydroxide a precipitate, strip the hafnium-containing loaded organic phase with a carbonate solution, mix the strip liquid with a base solution to give a hafnium hydroxide precipitate, roast the zirconium hydroxide precipitate and the hafnium hydroxide precipitate. The extraction agent comprises the mixture composed of DIBK and phosphonic acids extraction agent (containing C—P bond).

The embodiments of the present disclosure provide the following beneficial effects. A synergistic extraction system consisting of DIBK and a phosphonic acids extraction agent (containing C—P bond) has less mass transfer and large extraction capacity as its properties of preferential extraction of hafnium present at a relatively lower content in mixed solution of zirconium and hafnium. The process flow is simple and easy to operate. The extraction is efficient. Further, there is no need of use of highly toxic substances, e.g. thiocyanic acid or salts thereof in the separation. Therefore, the entire separation process is clean.

DETAILED DESCRIPTION OF EMBODIMENTS

To make the purposes, technical solutions and advantages of the present disclosure much clearer, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below. Examples for which no specific condition is indicated should be done under conventional conditions or a condition recommended by the manufacturer. All those agents or instruments for which no manufacturer is indicated are all conventional products which are commercially available.

Now the method for extracting zirconium and hafnium from nitric acid medium provided by the present disclosure will be described in detail as followings.

Zirconium and hafnium are symbiotic in the nature. As commercially available zirconium-containing chemicals normally contain a relatively low hafnium content (m_(Hf)/m_((Zr+Hf))) (generally at 1˜3%), It would be relatively largely advantageous to use an extraction agent by which hafnium is preferentially extracted in the separation. Due to “lanthanide contraction”, zirconium and hafnium have substantially identical atomic radius and ionic radius, and very similar physical and chemical properties, so it is very hard to separate them from each other. They are seen as two of the elements that are most difficult to separate in the periodic table of elements. However, zirconium and hafnium have different nuclear performances. With a small thermal neutron absorbing cross-section, zirconium is widely used as cladding and structure materials of nuclear reactor. It is required for nuclear grade zirconium that hafnium content should be lower than 0.01%. In contrast, hafnium has a large thermal neutron absorbing cross-section and is mainly used in the neutron control rod in the nuclear reaction. It is required for nuclear grade hafnium that zirconium content should be lower than 2%. Therefore, separating zirconium and hafnium is the key to obtain nuclear grade zirconium and nuclear grade hafnium materials.

As an aspect of the present disclosure, the embodiments of the present disclosure provide a method for extracting and separating zirconium and hafnium in nitric acid medium, which is mainly used to efficiently separate zirconium and hafnium and comprises the following steps.

There are many factors which may affect separation of zirconium and hafnium in the system where solvent extraction method is used to separate zirconium and hafnium in the present disclosure, comprising volume percentage content of the extraction agent, concentrations of zirconium and hafnium in the raw liquid, concentration of sulfate, concentration of chlorine ions, total acidity of free acids and molar concentration of carbonate in stripping. To improve the separation result, the concentration of each component in the prepared acidic raw liquid is controlled in some embodiments of the present disclosure, as follows.

If the zirconium ions and hafnium ions are present in the raw liquid at a total concentration lower than 0.05 mol/L, which may facilitate separation of zirconium and hafnium, but handling amount of the raw liquid would be relatively large and so is the total consumption amount of acids. If the zirconium ions and hafnium ions are present in the raw liquid at a total concentration higher than 2.0 mol/L, where the total acidity of free acids is less than 0.05 mol/L, the zirconium and hafnium are likely to hydrolyze, and the extractability of hafnium is relatively low, hence, the separation is not efficient; where the total acidity of free acids is more than 4.0 mol/L, the zirconium and hafnium separation coefficient decreases. To ensure a high separation efficiency of zirconium and hafnium, it is optimum that the zirconium ions and hafnium ions are present in the raw liquid at a total concentration of 0.05˜2.0 mol/L, preferably 0.5˜1.5 mol/L, more preferably 1.0˜1.5 mol/L.

The total acidity of free acids in the raw liquid is 2.0˜4.0 mol/L, preferably 2.5˜3.6 mol/L.

In addition, preferably, the concentration of nitrate ions in the acidic raw liquid is kept at 2.0˜4.0 mol/L, preferably 2.5˜3.5 mol/L. Optionally, inorganic salts may be introduced into the acidic raw liquid. Where sulfate is added to the acidic raw liquid as inorganic salt, sulfate ions may also be introduced. Preferably, the concentration of sulfate ions is kept at 0˜1.0 mol/L, e.g. concentration of sulfate ions being 0.2 mol/L, 0.4 mol/L, 0.5 mol/L, 0.6 mol/L, 0.8 mol/L, etc.

Optionally, ammonia liquor or the like may also be added to the acidic raw liquid to adjust the pH value of the acidic raw liquid.

Extraction is performed to the prepared acidic raw liquid with an extraction agent. The extraction agent comprises a synergistic extraction system consisting of DIBK and phosphonic acids extraction agent (containing C—P bond). The phosphonic acids extraction agent is at least one selected from the group consisting of Cyanex 921, Cyanex 923, Cyanex 925 and Cyanex 572. That is to say, the synergistic extraction system may be formed with DIBK and Cyanex 921, the synergistic extraction system may also be formed with DIBK and Cyanex 923, the synergistic extraction system may also be formed with DIBK and Cyanex 925, or the synergistic extraction system may also be formed with DIBK and Cyanex 572. In some embodiments of the present disclosure, the synergistic extraction system may also be formed with DIBK, and Cyanex 921, Cyanex 923, Cyanex 925 and Cyanex 572 together. Compared with liquid-liquid extraction using a single extraction agent, synergistic extraction is more efficient.

Diisobutyl ketone (DIBK) is a neutral oxygen-containing extraction agent. DIBK has a flash point of 47° C. and a water solubility of 0.043 wt %, and thus it is very low in water solubility.

In some embodiments of the present disclosure, in terms of extraction agent, where a synergistic extraction system is formed by mixing DIBK and phosphonic acids extraction agent (containing C—P bond), the phosphonic acids extraction agent (containing C—P bond) is present at a volume content preferably of 2˜40%, more preferably 2˜20%. It is also to be noted that in the synergistic extraction system, extraction agents with similar properties to Cyanex 921 or Cyanex 923 or Cyanex 925 or Cyanex 572 may be used to replace Cyanex 921 or Cyanex923 or Cyanex 925 or Cyanex 572, or other extraction agents with similar properties to them may further be added.

Phosphonic acids extraction agent (containing C—P bond) is an organic phosphine oxide-based extraction agent. When other factors are constant, as the volume percentage of phosphonic acids extraction agent (containing C—P bond) increases, the value of its zirconium-hafnium separation coefficient 13 increases first and then decreases. When the volume percentage concentration of the phosphonic acids extraction agent (containing C—P bond) is higher than 40%, the extraction amount of zirconium would be too large, which is bad for separation of zirconium and hafnium. Therefore, it is optimum that it is present at a content of 2˜20%.

The extraction may be done in a single-stage or multi-stage (e.g. 4˜20 stages) co-current and/or counter-current manner. The two phases are mixed for 2˜30 min, preferably 5˜15 min. The intra-tank temperature within the extraction tank is preferably kept within 0˜40° C., e.g. at 5° C., 10° C., 15° C., 20° C., 25° C., 30° C., 35° C., etc.

The study on the extraction mechanisms by which the reported MIBK system, DIBK-TBP system, DIBK-P204 system, DIBK-P350 system and DIBK-TOPO system work on zirconium and hafnium with of SCN⁻ suggests that the extracted complexes of zirconium are Zr(OH)₂(SCN)₂.2MIBK, Zr(SCN)₄.TBP.DIBK, Zr(SCN)₃.HA₂.DIBK, Zr(SCN)_(3.648).(HA₂)_(0.3520).(DIBK)_(0.0.1043) and Zr₄(OH)₈(H₂O)₁₀SCN₄Cl₄.4S.2B, respectively, (in which B represents DIBK and S represents TOPO), and that the extracted complexes of hafnium are Hf(OH)₂(SCN)₂.2MIBK, Hf(SCN)₄.TBP.DIBK, Hf(SCN)₃.HA₂.DIBK, Hf(SCN)_(2.6843).(HA₂)_(1.4157).(DIBK)_(0.689) and Hf₄(OH)₈(H₂O)₈SCN₈.4S.4B, respectively, which indicates that SCN⁻ is directly involved in the composition of the extracted complexes. Due to “lanthanide contraction”, Hf⁴⁺ has a radius (71×10⁻¹² m) slightly smaller than that of Zr⁴⁺ (72×10⁻¹² m). By Lewis's Soft-Hard-Acid-Base theory, both Hf⁴⁺ and Zr⁴⁺ are hard acids, but Hf⁴⁺ has a stronger acidity than Zr⁴⁺ and is more likely to form relatively stable complexes with hard basic extraction agents. The Lewis basicity of the extraction agents become stronger and stronger in the following order: R₂C═O<(RO)₃P═O<R₃P═O. This suggests that phosphonic acids extraction agents (containing C—P bond) are more likely to form relatively stable extracted complexes with Hf⁴⁺ having a small ion radius, compared to phosphoric acid-like extraction agents (containing C—O—P bond), that is, it is likely to be extracted. Therefore, a synergistic extraction system consisting of DIBK and a phosphonic acids extraction agent (containing C—P bond) may significantly improve the extraction rate of hafnium.

In some embodiments of the present disclosure, the extraction agent may be diluted in advance by mixing with a diluent which may be selected from sulfonated kerosene, hexane, isooctane, 200# solvent oil, etc. It should be understood that the diluent may consist of one or at least two of the above substances.

The extraction agent is mixed with nitric acid for pre-extraction. The nitric acid is preferably at a concentration of 3.0-6.0 mol/L, e.g. at 2.0 mol/L, 2.5 mol/L, 3.0 mol/L, 3.5 mol/L, 4.0 mol/L, 4.5 mol/L, 5.0 mol/L, 5.5 mol/L and 6.0 mol/L. The pre-extraction is done for enabling the extraction agent to reach pre-saturation state. In doing pre-extraction, the extraction agent is preferably isometric with the nitric acid.

After pre-extraction, the extraction agent serves as an organic phase, and the acidic raw liquid serves as an aqueous phase. They are mixed for extraction. After phase separation of extraction, zirconium is left in the raffinate and a zirconium solution containing little or no hafnium is obtained. The hafnium in the aqueous phase goes to the organic phase and hafnium-containing loaded organic phase is obtained.

The hafnium-free zirconium solution as obtained is subjected to precipitation with a base solution (e.g. ammonia liquor and caustic soda) to give zirconium hydroxide precipitate.

The hafnium-containing loaded organic phase is stripped with a carbonate solution. Optionally, the carbonate may be sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, ammonium carbonate, magnesium carbonate, aluminum carbonate, etc. In stripping, the carbonate may be one or the mixture of at least two of the above substances. After the stripping, hafnium goes to the aqueous phase. The resulting strip liquid is hafnium-rich solution. A m_(Hf)/m_((Hf+Zr)) weight ratio is 10˜40% in the resulting hafnium-rich solution. The concentration of the carbonate used in stripping may be e.g. 0.05˜5.0 mol/L.

Then the hafnium-rich solution is subjected to precipitation with a base solution (e.g. ammonia liquor and caustic soda) to give hafnium hydroxide precipitate.

The zirconium hydroxide precipitate and the hafnium hydroxide precipitate as obtained are washed with deionized water. The washed zirconium hydroxide precipitate and hafnium hydroxide precipitate are roasted. Preferably, the roasting is done at a temperature of 600˜2300° C., e.g. at 800° C., 1000° C., 1200° C., 1400° C., 1600° C. and 1800° C. The roasting may also be done under the temperature increasing in a gradient manner.

The zirconium oxide obtained from roasting is at the nuclear grade. The zirconium-containing hafnium oxide may also reach the nuclear grade after further separation.

As another aspect of the present disclosure, the embodiments of the present disclosure provide a method for extracting and separating zirconium and hafnium in nitric acid medium, which is mainly applied to efficient separation of zirconium and hafnium. This method is substantially same with the above separation method. The only difference lies in that the acidic raw liquid is prepared before extraction.

First, the raw material containing zirconium and hafnium to be separated is made into acidic raw liquid, that is, mixing the zirconium-containing chemical with nitric acid to form acidic raw liquid. Preferably, inorganic salt may be added to the acidic raw liquid. The inorganic salt may be at least one selected from the group consisting of ammonium chloride, sodium chloride, magnesium chloride, ammonium sulfate, sodium sulfate and magnesium sulfate.

In some embodiments of the present disclosure, a certain amount of ammonia liquor may also be added to the acidic raw liquid to adjust the pH value of the acidic raw liquid.

The acidic raw liquid may be prepared by the following methods:

I. carbonizing and chlorinating zirconite or directly subjecting zirconite to chlorination under boiling to prepare zirconium tetrachloride; and dissolving the zirconium tetrachloride in water, to which ammonia liquor and inorganic salt are added to make acidic raw liquid, wherein the ammonia liquor and inorganic salt may be added in predetermined amounts;

II. subjecting zirconite to alkali fusion, washing, and leaching it with diluted hydrochloric acid to give solution, to which hydrochloric acid and inorganic salt are added in predetermined amounts to make acidic raw liquid;

III. directly dissolving zirconium oxychloride in water and adding hydrochloric acid and inorganic salt in predetermined amounts to make acidic raw liquid; or

IV. preparing raw liquid by the first or second method with zirconium oxide, zirconium metal, hafnium oxide, hafnium metal, or raw material of zirconium waste containing other impurities or hafnium waste containing other impurities, to which nitric acid and inorganic salt are added in predetermined amounts to make acidic raw liquid.

Table 1 basically shows the compositions of the raw liquid, in the acidic raw liquid prepared by the above methods.

TABLE 1 Compositions of acidic raw liquid Component Total concentration of Total acidity zirconium and hafnium Hafnium content of free acids Nitrate ions Sulfate ions (mol/L) (m_(Hf)/m_((Hf+Zr)) %) (mol/L) (mol/L) (mol/L) Concentration 0.05~2.0 0.5~97.0 2.0~4.0 2.0~4.0 0~1.25

Now the characteristics and effects of the present disclosure will be further described in detail in combination of the Examples as followings.

Example 1

A method for separating zirconium and hafnium, comprising the following steps:

(1) Preparing acidic raw liquid: the aqueous phase contains zirconium and hafnium ions at an initial total concentration of 1.5 mol/L; the hafnium ions are present at a concentration of 0.018 mol/L; the aqueous phase has an acidity of 2.87 mol/L; (NH₄)₂SO₄ is present at a concentration of 0.8 mol/L.

(2) The mixed organic phase consisting of 90% (v/v) of DIBK and 10% (v/v) of Cyanex923 is used as the extraction agent. First, pre-extraction is performed to the extraction agent and 5.5 mol/L nitric acid with equal volume. Then the extraction agent after pre-extraction is used as the organic phase, and the acidic raw liquid is used as the aqueous phase. The phase ratio (organic phase/aqueous phase) is kept at 2:1. Single-stage extraction is performed to the raw liquid at room temperature, with mixing time of the two phases being 10 min. Zirconium is left in the aqueous phase, and zirconium solution containing little hafnium is obtained. Then the zirconium solution is subjected to precipitation with ammonia liquor to give zirconium hydroxide precipitate, and all hafnium in the aqueous phase is extracted to the organic phase to give hafnium-containing loaded organic phase.

(3) The loaded organic phase is stripped with 1.0 mol/L potassium carbonate, wherein the phase ratio (organic phase/aqueous phase) in stripping is kept at 1:2 and the mixing time of the two phases is 10 min, to obtain hafnium-rich solution containing zirconium. Then precipitation is performed with ammonia liquor to give hafnium hydroxide precipitate.

(4) The zirconium hydroxide precipitate and the hafnium hydroxide precipitate are washed with deionized water, respectively. The washed zirconium hydroxide precipitate and hafnium hydroxide precipitate are roasted at 1,000° C. to give zirconium oxide containing little hafnium and hafnium oxide product containing little zirconium.

The total concentrations of zirconium and hafnium metal ions in the aqueous phase before and after the extraction are measured by titrimetry method with standard EDTA solution. The acidity is measured by titrimetry method with standard sodium hydroxide solution. The hafnium concentration is measured by inductively coupled plasma mass spectrometry (ICP-MS). The total concentration of zirconium and hafnium metal ions and the concentration of hafnium ions in the organic phase are calculated by the subtraction method, respectively. The distribution ratio, separation coefficient and extraction rate are calculated one by one.

The concentrations of metal ions in the organic phase, the distribution ratios and zirconium and hafnium, the separation coefficient and the extraction rates are calculated by the following formulas, respectively.

$\begin{matrix} {\lbrack{Zr}\rbrack_{o} = \frac{\left( {C_{Zr}^{0} - \lbrack{Zr}\rbrack_{a}} \right) \times V_{a}}{V_{o}}} & (1) \\ {\lbrack{Hf}\rbrack_{o} = \frac{\left( {C_{Hf}^{0} - \lbrack{Hf}\rbrack_{a}} \right) \times V_{a}}{V_{o}}} & (2) \\ {D_{r{({Zr})}} = {\frac{\lbrack{Zr}\rbrack_{eo}}{\lbrack{Zr}\rbrack_{ea}} = \frac{C_{Zr}^{0} - \lbrack{Zr}\rbrack_{ea}}{\lbrack{Zr}\rbrack_{ea}}}} & (3) \\ {D_{r{({Hf})}} = {\frac{\lbrack{Hf}\rbrack_{eo}}{\lbrack{Hf}\rbrack_{ea}} = \frac{C_{Hf}^{0} - \lbrack{Hf}\rbrack_{ea}}{\lbrack{Hf}\rbrack_{ea}}}} & (4) \\ {\beta = \frac{D_{r{({Hf})}}}{D_{r{({Zr})}}}} & (5) \\ {E_{Zr} = {\frac{C_{Zr}^{0} - \lbrack{Zr}\rbrack_{ea}}{C_{Zr}^{0}} \times 100\%}} & (6) \\ {E_{Hf} = {\frac{C_{Hf}^{0} - \lbrack{Hf}\rbrack_{ea}}{C_{Hf}^{0}} \times 100\%}} & (7) \end{matrix}$

In the above formulas [Zr]_(o) and [Hf]_(o) represent the concentrations of zirconium and hafnium in the organic phase, respectively, in g/L;

[Zr]_(a) and [Hf]_(a) represent concentrations of zirconium and hafnium in the aqueous phase, respectively, in g/L;

C_(Zr) ⁰ and C_(Hf) ⁰ represent initial concentrations of zirconium and hafnium ions in the aqueous phase, respectively, in g/L;

V_(a) and V_(o) represent volumes of the aqueous phase and the organic phase, respectively, in mL;

D_(r(Zr)) and D_(r(Hf)) represent the distribution ratios of zirconium and hafnium, respectively;

[Zr]_(ea), [Hf]_(ea) represent concentrations of zirconium and hafnium ions in the aqueous phase at the time of equilibrium, respectively, in g/L;

[Zr]_(eo), [Hf]_(eo) represent concentrations of zirconium and hafnium ions in the organic phase at the time of equilibrium, respectively, in g/L;

β represents the separation coefficient of zirconium and hafnium; and

E_(Zr) and E_(Hf) represent the extraction rates of the organic phase for zirconium and hafnium, respectively.

By calculation, in the present example, the extraction rate for hafnium is 87.77%, and 15.99% for zirconium. The separation coefficient of zirconium and hafnium is up to 37.

Example 2

The organic phase consisted of 90% (v/v) of DIBK, 2% (v/v) of Cyanex921 and 8% (v/v) of isooctane (as diluent) and is subjected to pre-extraction in the presence of 6.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 1.5 mol/L. The concentration of hafnium ions was 0.018 mol/L. The acidity of the aqueous phase was 3.0 mol/L. (NH₄)₂SO₄ was added in an amount of 1.0 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with mixing time of the two phases being 5 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate. The loaded organic phase was stripped with 1.0 mol/L potassium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 5 min, to obtain hafnium-rich solution containing zirconium. Ammonia liquor was added for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 66.52%, and 11.53% for zirconium. The separation coefficient of zirconium and hafnium is up to 10.

Example 3

The organic phase consisted of 90% (v/v) of DIBK, 8% (v/v) of Cyanex923 and 2% (v/v) of sulfonated kerosene (as diluent) and is subjected to pre-extraction in the presence of 6.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 1.5 mol/L. The concentration of hafnium ions was 0.018 mol/L. The acidity of the aqueous phase was 3.0 mol/L. (NH₄)₂SO₄ was added in an amount of 0.8 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with mixing time of the two phases being 5 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 1.0 mol/L sodium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 5 min, to obtain hafnium-rich solution containing zirconium. Ammonia liquor was added for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 84.98%, and 16.51% for zirconium. The separation coefficient of zirconium and hafnium is up to 20.

Example 4

The organic phase consisted of 60% (v/v) of DIBK and 40% (v/v) of Cyanex925 and is subjected to pre-extraction in the presence of 4.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 0.05 mol/L. The concentration of hafnium ions was 0.0006 mol/L. The acidity of the aqueous phase was 2.0 mol/L. (NH₄)₂SO₄ was added in an amount of 0.2 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with mixing time of the two phases being 2 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Sodium hydroxide was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 3.0 mol/L potassium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 5 min, to obtain hafnium-rich solution containing zirconium. m_(Hf)/m_((Hf+Zr)) weight ratio was 18% in the hafnium-rich solution. Ammonia liquor was used for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 72.06%, and 16.29% for zirconium. The separation coefficient of zirconium and hafnium is up to 13.

Example 5

The organic phase consisted of 80% (v/v) of DIBK and 20% (v/v) of Cyanex923 and is subjected to pre-extraction in the presence of 3.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 1.5 mol/L. The concentration of hafnium ions was 0.018 mol/L. The acidity of the aqueous phase was 1.5 mol/L. NH₄Cl was added in an amount of 1.25 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 30 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 2.0 mol/L magnesium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 5 min, to obtain hafnium-rich solution containing zirconium. m_(Hf)/m_((Hf+Zr)) weight ratio was 10% in the hafnium-rich solution. Ammonia liquor was used for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 35.74%, and 17.25% for zirconium. The separation coefficient of zirconium and hafnium is up to 6.

Example 6

The organic phase consisted of 70% (v/v) of DIBK and 30% (v/v) of Cyanex923 and is subjected to pre-extraction in the presence of 5.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 2.0 mol/L. The concentration of hafnium ions was 0.024 mol/L. The acidity of the aqueous phase was 2.5 mol/L. MgCl₂ was added in an amount of 1.0 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 25 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Potassium hydroxide was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 2.0 mol/L aluminum carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 25 min, to obtain hafnium-rich solution containing zirconium. m_(Hf)/m_((Hf+Zr)) weight ratio was 30% in the hafnium-rich solution. Ammonia liquor was used for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 79.72%, and 17.02% for zirconium. The separation coefficient of zirconium and hafnium is up to 18.

Example 7

The organic phase consisted of 95% (v/v) of DIBK and 5% (v/v) of Cyanex923 and is subjected to pre-extraction in the presence of 6.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 0.5 mol/L. The concentration of hafnium ions was 0.006 mol/L. The acidity of the aqueous phase was 3.0 mol/L. (NH₄)₂SO₄ was added in an amount of 0.8 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 10 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 3.0 mol/L sodium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 10 min, to obtain hafnium-rich solution containing zirconium. m_(Hf)/m_((Hf+Zr)) weight ratio was 10% in the hafnium-rich solution. Ammonia liquor was used for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 66.52%, and 21.46% for zirconium. The separation coefficient of zirconium and hafnium is up to 6.

Example 8

The organic phase consisted of 65% (v/v) of DIBK and 35% (v/v) of Cyanex923 and is subjected to pre-extraction in the presence of 6.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 1.5 mol/L. The concentration of hafnium ions was 0.018 mol/L. The acidity of the aqueous phase was 3.0 mol/L. (NH₄)₂SO₄ was added in an amount of 0.8 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 15 min. Ammonia liquor was added for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 1.0 mol/L sodium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 15 min to obtain hafnium-rich solution containing zirconium. m_(Hf)/m_((Hf+Zr)) weight ratio was 40% in the hafnium-rich solution. Ammonia liquor was used for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 86.08%, and 16.05% for zirconium. The separation coefficient of zirconium and hafnium is up to 34.

Example 9

The organic phase consisted of 90% (v/v) of DIBK, 2% (v/v) of Cyanex923 and 8% (v/v) of hexane and is subjected to pre-extraction in the presence of 2.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 1.0 mol/L. The concentration of hafnium ions was 0.012 mol/L. The acidity of the aqueous phase was 1.0 mol/L. (NH₄)₂SO₄ was added in an amount of 0.6 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 5 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 2.5 mol/L sodium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 5 min, to obtain hafnium-rich solution containing zirconium. Ammonia liquor was added for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 49.80%, and 13.68% for zirconium. The separation coefficient of zirconium and hafnium is up to 6.

Example 10

The organic phase consisted of 90% (v/v) of DIBK, 8% (v/v) of Cyanex923 and 2% (v/v) of isooctane and is subjected to pre-extraction in the presence of 5.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 2.0 mol/L. The concentration of hafnium ions was 0.024 mol/L. The acidity of the aqueous phase was 2.5 mol/L. (NH₄)₂SO₄ was added in an amount of 1.0 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 10 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 1.5 mol/L sodium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 10 min, to obtain hafnium-rich solution containing zirconium. Ammonia liquor was added for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 72.15%, and 16.66% for zirconium. The separation coefficient of zirconium and hafnium is up to 12.

Example 11

The organic phase consisted of 90% (v/v) of DIBK and 10% (v/v) of Cyanex572 and is subjected to pre-extraction in the presence of 4.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 1.5 mol/L. The concentration of hafnium ions was 0.018 mol/L. The acidity of the aqueous phase was 2.0 mol/L. (NH₄)₂SO₄ was added in an amount of 0.8 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with mixing time of the two phases being 10 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate. The loaded organic phase was stripped with 1.0 mol/L sodium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 10 min to obtain hafnium-rich solution containing zirconium. Ammonia liquor was added for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 66.96%, and 8.68% for zirconium. The separation coefficient of zirconium and hafnium is up to 26.

Example 12

The organic phase consisted of 90% (v/v) of DIBK, 2% (v/v) of Cyanex572 and 8% (v/v) of sulfonated kerosene (as diluent) and is subjected to pre-extraction in the presence of 4.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 1.5 mol/L. The concentration of hafnium ions was 0.018 mol/L. The acidity of the aqueous phase was 2.0 mol/L. (NH₄)₂SO₄ was added in an amount of 0.6 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 5 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate. The loaded organic phase was stripped with 1.0 mol/L potassium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 5 min, to obtain hafnium-rich solution containing zirconium. Ammonia liquor was added for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 60.44%, and 8.62% for zirconium. The separation coefficient of zirconium and hafnium is up to 10.

Example 13

The organic phase consisted of 90% (v/v) of DIBK, 8% (v/v) of Cyanex923 and 2% (v/v) of Cyanex925 and is subjected to pre-extraction in the presence of 6.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 1.5 mol/L. The concentration of hafnium ions was 0.018 mol/L. The acidity of the aqueous phase was 3.0 mol/L. (NH₄)₂SO₄ was added in an amount of 0.8 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 5 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 1.0 mol/L sodium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 5 min, to obtain hafnium-rich solution containing zirconium. Ammonia liquor was added for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 84.46%, and 15.71% for zirconium. The separation coefficient of zirconium and hafnium is up to 30.

Example 14

The organic phase consisted of 60% (v/v) of DIBK and 40% (v/v) of Cyanex572 and is subjected to pre-extraction in the presence of 4.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 1.0 mol/L. The concentration of hafnium ions was 0.012 mol/L. The acidity of the aqueous phase was 2.0 mol/L. (NH₄)₂SO₄ was added in an amount of 1.25 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 2 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Sodium hydroxide was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 2.0 mol/L potassium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 5 min, to obtain hafnium-rich solution containing zirconium. m_(Hf)/m_((Hf+Zr)) weight ratio was 30% in the hafnium-rich solution. Ammonia liquor was used for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 66.06%, and 9.26% for zirconium. The separation coefficient of zirconium and hafnium is up to 20.

Example 15

The organic phase consisted of 80% (v/v) of DIBK and 20% (v/v) of Cyanex921 and is subjected to pre-extraction in the presence of 3.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 2.0 mol/L. The concentration of hafnium ions was 0.024 mol/L. The acidity of the aqueous phase was 1.5 mol/L. NH₄Cl was added in an amount of 1.0 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 30 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 1.0 mol/L magnesium carbonate, wherein, the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 5 min, to obtain hafnium-rich solution containing zirconium. m_(Hf)/m_((Hf+Zr)) weight ratio was 10% in the hafnium-rich solution. Ammonia liquor was used for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 35.52%, and 17.20% for zirconium. The separation coefficient of zirconium and hafnium is up to 6.

Example 16

The organic phase consisted of 70% (v/v) of DIBK and 30% (v/v) of Cyanex925 and is subjected to pre-extraction in the presence of 5.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 2.0 mol/L. The concentration of hafnium ions was 0.024 mol/L. The acidity of the aqueous phase was 2.5 mol/L. MgCl₂ was added in an amount of 0.6 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 25 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Potassium hydroxide was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 1.0 mol/L aluminum carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 25 min, to obtain hafnium-rich solution containing zirconium. m_(Hf)/m_((Hf+Zr)) weight ratio was 25% in the hafnium-rich solution. Ammonia liquor was used for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 70.16%, and 16.66% for zirconium. The separation coefficient of zirconium and hafnium is up to 15.

Example 17

The organic phase consisted of 90% (v/v) of DIBK and 5% (v/v) of Cyanex572 and is subjected to pre-extraction in the presence of 3.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 0.5 mol/L. The concentration of hafnium ions was 0.006 mol/L. The acidity of the aqueous phase was 1.5 mol/L. (NH₄)₂SO₄ was added in an amount of 0.8 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 10 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 2.0 mol/L sodium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 10 min, to obtain hafnium-rich solution containing zirconium. m_(Hf)/m_((Hf+Zr)) weight ratio was 20% in the hafnium-rich solution. Ammonia liquor was used for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 56.42%, and 8.28% for zirconium. The separation coefficient of zirconium and hafnium is up to 10.

Example 18

The organic phase consisted of 65% (v/v) of DIBK and 35% (v/v) of Cyanex572 and is subjected to pre-extraction in the presence of 4.4 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 1.0 mol/L. The concentration of hafnium ions was 0.012 mol/L. The acidity of the aqueous phase was 2.2 mol/L. (NH₄)₂SO₄ was added in an amount of 0.8 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 15 min. Ammonia liquor was added for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 1.0 mol/L sodium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 15 min, to obtain Hafnium-rich solution containing zirconium. m_(Hf)/m_((Hf+Zr)) weight ratio was 30% in the hafnium-rich solution. Ammonia liquor was used for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 70.84%, and 9.04% for zirconium. The separation coefficient of zirconium and hafnium is up to 22.

Example 19

The organic phase consisted of 90% (v/v) of DIBK, 2% (v/v) of Cyanex921 and 8% (v/v) of hexane and is subjected to pre-extraction in the presence of 2.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 2.0 mol/L. The concentration of hafnium ions was 0.024 mol/L. The acidity of the aqueous phase was 1.0 mol/L. (NH₄)₂SO₄ was added in an amount of 0.8 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 5 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 2.0 mol/L sodium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 5 min, to obtain hafnium-rich solution containing zirconium. Ammonia liquor was added for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 49.45%, and 13.24% for zirconium. The separation coefficient of zirconium and hafnium is up to 7.

Example 20

The organic phase consisted of 90% (v/v) of DIBK, 8% (v/v) of Cyanex572 and 2% (v/v) of isooctane and is subjected to pre-extraction in the presence of 4.0 mol/L nitric acid at a volume equal to the organic phase in advance for one time. The aqueous phase contained zirconium and hafnium ions at an initial total concentration of 2.0 mol/L. The concentration of hafnium ions was 0.024 mol/L. The acidity of the aqueous phase was 2.0 mol/L. (NH₄)₂SO₄ was added in an amount of 0.8 mol/L. The phase ratio was kept at 2:1. Single-stage extraction was done at room temperature, with the mixing time of the two phases being 10 min. Raffinate and hafnium-containing loaded organic phase were obtained after phase separation. Ammonia liquor was added to the raffinate for precipitation to give zirconium hydroxide precipitate containing little hafnium. The loaded organic phase was stripped with 1.0 mol/L sodium carbonate, wherein the phase ratios for both washing and stripping were 1:2 and the mixing time of the two phases was 10 min, to obtain hafnium-rich solution containing zirconium. Ammonia liquor was added for precipitation to give hafnium hydroxide precipitate containing zirconium. The other operation steps are same as Example 1.

By calculation, in the present example, the extraction rate for hafnium is 64.22%, and 8.56% for zirconium. The separation coefficient of zirconium and hafnium is up to 15.

Example 21

The present example differs from Example 1 in that the synergistic extraction system used is different. In the present example, the used synergistic extraction system consisted of 90% (v/v) of DIBK, 5% (v/v) of Cyanex923 and 5% (v/v) of Cyanex572. The ratio of other raw materials and the preparation method are all the same to the above examples.

The examples described above are only some but not all of the examples of the present disclosure. Hence, the detailed description of the examples of the present disclosure is not intended to limit the scope of the disclosure as claimed, but merely shows the selected examples of the present disclosure. All the other embodiments obtained by those ordinarily skilled in the art based on the embodiments provided in the present disclosure without paying creative efforts shall fall within the scope of protection of the present disclosure. 

1. A method for extracting and separating zirconium and hafnium in a nitric acid medium, comprising following steps of: performing extraction by mixing an extraction agent with an acidic raw liquid formed by mixing a zirconium-containing chemical and nitric acid, mixing a raffinate, which is obtained after phase separation caused by the extraction, with a base to give zirconium hydroxide precipitate, stripping hafnium-containing loaded organic phase with a carbonate solution, mixing a liquid obtained after the stripping with a base solution to give hafnium hydroxide precipitate, and roasting the zirconium hydroxide precipitate and the hafnium hydroxide precipitate, wherein the extraction agent comprises a mixture consisting of diisobutyl ketone (DIBK) and phosphonic acids extraction agent.
 2. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 1, wherein free acids are present in the acidic raw liquid at a total acidity of 2.0˜4.0 mol/L; and/or zirconium ions and hafnium ions are present in the acidic raw liquid at a total concentration of 0.05˜2.0 mol/L.
 3. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 2, wherein nitrate ions are present in the acidic raw liquid at a concentration of 2.0˜4.0 mol/L; and/or sulfate ions are present at a concentration of 0˜1.0 mol/L.
 4. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 1, wherein the inorganic salt is at least one selected from the group consisting of ammonium chloride, sodium chloride, magnesium chloride, ammonium sulfate and sodium sulfate.
 5. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 1, wherein the phosphonic acids extraction agent accounts for 2˜40% (v/v) by volume; and/or m_(Hf)/m_((Hf+Zr)) weight ratio is 10˜40% in the liquid after the stripping.
 6. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 5, wherein the extraction agent is mixed with a diluent before the extraction.
 7. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 1, wherein the extraction is performed in a single-stage or multi-stage co-current manner and/or a single-stage or multi-stage counter-current manner.
 8. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 1, wherein the carbonate is at least one selected from the group consisting of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, ammonium carbonate, magnesium carbonate and aluminum carbonate.
 9. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 1, wherein the roasting is performed under a condition of 600˜2300° C., and/or the zirconium hydroxide precipitate and the hafnium hydroxide precipitate are washed before roasting.
 10. A method for extracting and separating zirconium and hafnium in a nitric acid medium, comprising mixing a zirconium-containing chemical and nitric acid to form an acidic raw liquid, and performing extraction on the acidic raw liquid with an extraction agent to give a raffinate and a hafnium-containing loaded organic phase after phase separation of the extraction, mixing the raffinate with a base solution to give a zirconium hydroxide precipitate, stripping the hafnium-containing loaded organic phase with a carbonate solution, mixing a liquid obtained after stripping with a base solution to give a hafnium hydroxide precipitate, and roasting the zirconium hydroxide precipitate and the hafnium hydroxide precipitate, wherein the extraction agent comprises a mixture consisting of DIBK and phosphonic acids extraction agent.
 11. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 1, wherein the phosphonic acids extraction agent is at least one selected from the group consisting of Cyanex 921, Cyanex 923, Cyanex 925 and Cyanex
 572. 12. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 1, wherein the extraction agent is pre-extracted with nitric acid before the extraction.
 13. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 1, wherein the nitric acid has a concentration of 2.0˜6.0 mol/L in the pre-extraction, and/or the extraction agent has a volume equal to that of the nitric acid in the pre-extraction.
 14. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 1, wherein the acidic raw liquid further comprises an inorganic salt.
 15. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 2, wherein free acids are present in the acidic raw liquid at a total acidity of 2.5˜3.6 mol/L.
 16. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 2, wherein zirconium ions and hafnium ions are present in the acidic raw liquid at a total concentration of 0.5˜1.5 mol/L.
 17. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 3, wherein nitrate ions are present in the acidic raw liquid at a concentration of 2.5˜3.5 mol/L.
 18. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 5, wherein the phosphonic acid-like extraction agent accounts for 2˜20% (v/v) by volume in the extraction agent.
 19. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 6, wherein the diluent is at least one selected from the group consisting of sulfonated kerosene, hexane, isooctane and 200# solvent oil.
 20. The method for extracting and separating zirconium and hafnium in a nitric acid medium according to claim 7, wherein two phases are mixed for 2˜30 min. 